Russia's largest oil company, Rosneft, says it has opened a new oil field in the Kara Sea region of the Arctic Ocean with U.S. partner ExxonMobil.

The announcement comes after the United States targeted Rosneft and its chief Igor Sechin with sanctions over Moscow's role in the Ukraine conflict.

Rosneft said in a statement September 27 that the estimated deposits exceed 100 million tons of light crude oil.

Light crude oil is has a low density and is more expensive than heavy crude oil because it produces a higher percentage of gasoline and diesel fuel when refined.

It said the new field, named Pobeda (Victory), also contains an estimated 338 million cubic meters of gas.

However, it remained unclear if commercially viable quantities of oil could be recovered from the well and its discovery came as ExxonMobil prepared to "wind down" the project following the U.S. sanctions.

The drilling at the Universitetskaya-1 well is part of a joint venture with ExxonMobil, a $3.2-billion deal Rosneft signed with the U.S. company in 2011.

The U.S. Treasury Department gave companies until September 26 to bring to an end exploration or production projects in deep water, Arctic offshore or extraction of shale gas or oil with Rosneft and four other Russian energy companies.

ExxonMobil was able to get a 14-day extension to wrap-up its work in Russia.

Sechin said during a September 27 visit to the site that Rosneft's partners who must leave projects due sanctions would have an option to return.

"We are not looking at the possibility of inviting new partners. We prefer stability in our work," Sechin said.

Prior to the sanctions, Rosneft's strategic plan for the next decade envisioned opening a series of new oil and gas fields in the northern seas above Russia.

However, Russian companies do not have the necessary technology and equipment to realize these projects so the departure of companies such as ExxonMobil sets back Rosneft's timetable for commercial production, whih was already not expected to start until the middle of the next decade.

Sechin also confirmed the Rosneft has requested a commercial loan from the Russian government to be used in developing projects in East Siberia and the Far East.

Based on reporting by Interfax, ITAR-TASS, AFP, Reuters, Caspian Barrel, and RIA Novosti